1. Field of the Invention
The present invention relates to an apparatus and a method for controlling a relay in electric drive vehicles, and in particular, to an apparatus and a method for controlling a relay of electric drive vehicles in a situation requiring turn-off of the relay.
2. Description of the Related Art
Vehicles using fossil fuel, such as gasoline, diesel and so on, generate a lot of harmful exhaust gases and pollute the air. The harmful exhaust gas is one of factors affecting global warming and exerts an injurious effect upon global environment. To solve this problem, attempts have been made to develop vehicles reducing fossil fuel consumption or running on alternative fuel. While making such attempts, interests are centered on HEVs (Hybrid Electrical Vehicles) or EVs (Electrical Vehicles) capable of running on an electrical energy supplied from a high-capacity battery pack.
HEVs can run by a motor driven by an electrical energy supplied from a battery pack as well as by an engine consuming fossil fuel. HEVs are controlled to maximum fuel efficiency conforming to driving conditions on the basis of these two types of power sources.
At the time of applying the brake or reducing the speed of HEVs, a driving motor of HEVs is converted from a power mode to a generation mode under the control of HCU (Hybrid Control Unit). Then, the battery pack is charged with an electrical energy produced from a generator (or a driving motor) under the control of BMS (Battery Management System) connected with the HCU.
In a power mode, a driving current is applied from the battery pack to an electric drive unit such as a driving motor, to drive the vehicle or operate the electric drive unit.
In a high-voltage battery system used in large electric loads such as HEVs or the like, a high-voltage relay is turned on only when a battery is used, due to the risk of electric shock. That is to say, when the use of the battery is terminated, or when an emergency occurs such as malfunction of BMS, the relay is turned off to prevent electric shock.
However, at the time of turning off the high-voltage relay, if a residual current exists between the high-voltage battery and the driving motor, in-flow of a surge current may cause damage to the high-voltage relay. If this phenomenon is repeated many times, the high-voltage relay may break, resulting in damage or injury to vehicles or passengers.